1. Field of the Invention
The present invention relates generally to magnetic recording and/or reproducing apparatuses having a rotary head tracking control device, and more particularly to a magnetic recording and/or reproducing apparatus having a device for performing tracking control of the rotary head so that the rotary head accurately follows and traces the skews in the track on the magnetic tape upon reproduction, in which the height position of the rotary head is always controlled to be constant upon recording.
2. Prior Art
In recent years, in magnetic recording and/or reproducing apparatuses such as video tape recorders (VTR) of the helical scan type for home use, there has been a trend toward even higher densities of recording and reproducing, aided by improvements in magnetic tapes. For example, by reducing the tape speed and track pitch to approximately 1/3, for example, of their values as compared to the case of the conventional recording and/or reproducing capacity of 2 hours, recording and reproducing of 6 hours can be carried out. Susch long-duration recording and/or reproducing techniques are being reduced to practice. However, in the VTR for home use, in which the tape travel system is simplified in order to lower the cost, it is difficult to reproduce a magnetic tape having a reduced track pitch as mentioned above while positively maintaining the required tracking precision.
Furthermore, in a magnetic recording/reproducing apparatus capable of recording/reproducing for 2 hours, it is necessary to manipulate a tracking knob in order to cause the magnetic head to undergo accurate tracking along a track of the magnetic tape when interchanged reproduction is performed with another apparatus. That is, in the case where there are (1) differences in the position of the control head, (2) differences in the height of the video head, and (3) skews in the video track, between the recording and reproducing apparatuses, an optimum tracking state is not obtained, and hence maximum output cannot be obtained at the time of this interchanged reproduction.
For example, in the case where the distance L from the position where a video head which is mounted on the rotary drum begins to make contact with the magnetic tape to the position of the control head is longer than a standard value in the recorder, the tracking phase deviates. In this case, a control pulse is recorded by the control head at the lower edge of the magnetic tape. In a magnetic recording and/or reproducing apparatus capable of carrying out recording and reproducing of 6 hours, for example, the recording interval of the control pulse is 0.37 millimeters, which is approximately 1/3 of the 1.11 millimeters, obtained in the case of a conventional recording and reproducing of 2 hours.
In the case where the above mentioned distance L is not coincident with the standard value, it is necessary to adjust the tracking knob to delay the reproducing control signal by a required time to thereby carry out normal tracking. However, adjustment of the tracking knob requires an operation in which, as the reproduced picture is observed, the knob is finely adjusted in a manner such that noise is not generated, and this manipulation is complicated.
Furthermore, while the rotational control of the rotary drum and the rotating magnetic heads carried out by means of a drum servo-control by reproducing the above mentioned control pulses accomplishes a control function of a degree such as to maintain the relative positions of the corresponding positional relationship between each track and the rotating video heads, this rotational control, in the prior art, has not accomplished the function of a so-called tracking control.
Accordingly, a device for performing tracking control has been proposed in the U.S. patent application Ser. No. 178,852, for example, in which a new type of head moving mechanism for varying the height position of the rotary head is provided, and the head moving mechanism is controlled according to the tracking error of the rotary head, so that the rotary head finely follows and traces the track even when skews exist in the track on the magnetic tape. By using this proposed device, tracking control can be performed even upon reproduction modes in which the tape travelling speed is different from that upon recording, as in a slow-motion, fast-motion, and still reproduction modes, and a fine reproduced signal can be obtained having little noise accompanied by the tracking error.
Furthermore, the above proposed head moving mechanism is of a new construction in which the principle of a see-saw operation is employed, however, a head moving mechanism using bimorph has been used conventionally.
In a magnetic recording and/or reproducing apparatus provided with this type of a tracking control device, upon recording mode, it is necessary to maintain and support the rotary head at a predetermined constant height position in order to form tracks with a constant pitch and record signals. Accordingly, a constant voltage was conventionally applied to the head moving mechanism, to maintain the height position of the rotary head to be constant.
However, the rotary head is generally rotated at a high speed, of the order of 30 revolutions per second, and thus, the rotary head undergoes microscopic displacement even if a measure is taken to simply apply a constant voltage to the head moving mechanism. It is very difficult to constantly and accurately form tracks at a constant pitch, especially when the track pitch is small. Moreover, especially in a simplified magnetic recording and/or reproducing apparatus, it is difficult to provide a mechanism spearately to strongly lock the head moving mechanism so that the head moving mechanism does not move during the recording mode.
Therefore, in a magnetic recording and/or reproducing apparatus having the above described head moving mechanism, the realization to always maintain the height position of the rotary head to be constant in the recording mode, was highly desired.
Thus, another system has been proposed conventionally in which, reproduction is performed within a vertical blanking period of a video signal which is recorded on a magnetic tape, upon recording mode, throughout a period of 1.5 H (H designates one horizontal scanning period), for example, to indirectly detect the height position of the rotary head by detecting the cross-talk level from the adjacent tracks, and control the height position of the rotary head to be constant according to the detected information. However, in this proposed system, since reproduction is performed within the above period during the recording mode, drop-out of information is introduced in the recorded signal during the above period, and was disadvantageous in that interference is introduced in positively obtaining vertical synchronization.